The technology of the present disclosure relates generally to distributed antenna systems (DASs), and more particularly to frequency shifting a communications signal(s) in a multiple frequency (multi-frequency) DAS to avoid or reduce potential frequency band interference, such as due to out-of-band harmonics generated by non-linearities in signal processing components.
Wireless communication is rapidly growing, with ever-increasing demands for high-speed mobile data communication. As an example, local area wireless services (e.g., so-called “wireless fidelity” or “WiFi” systems) and wide area wireless services are being deployed in many different types of areas (e.g., coffee shops, airports, libraries, etc.). Distributed communications or antenna systems communicate with wireless devices called “clients,” “client devices,” or “wireless client devices,” which must reside within the wireless range or “cell coverage area” in order to communicate with an access point device. Distributed antenna systems are particularly useful to be deployed inside buildings or other indoor environments where client devices may not otherwise be able to effectively receive radio-frequency (RF) signals from a source, such as a base station for example. Example applications where distributed antenna systems can be used to provide or enhance coverage for wireless services include public safety, cellular telephony, wireless local access networks (LANs), location tracking, and medical telemetry inside buildings and over campuses.
One approach to deploying a distributed antenna system involves the use of RF antenna coverage areas, also referred to as “antenna coverage areas.” Antenna coverage areas can be formed by remotely distributed antenna units, also referred to as remote units (RUs). The remote units each contain or are configured to couple to one or more antennas configured to support the desired frequency(ies) or polarization to provide the antenna coverage areas. Antenna coverage areas can have a radius in the range from a few meters up to twenty meters as an example. Combining a number of remote units creates an array of antenna coverage areas. Because the antenna coverage areas each cover small areas, there typically may be only a few users (clients) per antenna coverage area. This arrangement generates a uniform high quality signal enabling high throughput supporting the required capacity for the wireless system users.
As an example, FIG. 1 illustrates distribution of communications services to coverage areas 10(1)-10(N) of a DAS 12, wherein ‘N’ is the number of coverage areas. These communications services can include cellular services, wireless services such as RFID tracking, Wireless Fidelity (WiFi), local area network (LAN), WLAN, and combinations thereof, as examples. The coverage areas 10(1)-10(N) may be remotely located. In this regard, the remote coverage areas 10(1)-10(N) are created by and centered on remote antenna units 14(1)-14(N) connected to a central unit 16 (e.g., a head-end controller or head-end unit). The central unit 16 may be communicatively coupled to a base station 18. If the DAS 12 is a broadband DAS, the central unit 16 receives downlink communications signals 20D in multiple frequency bands for different communications services from the base station 18 to be distributed to the remote antenna units 14(1)-14(N). The remote antenna units 14(1)-14(N) are configured to receive downlink communications signals 20D from the central unit 16 over a communications medium 22 to be distributed as downlink communications signals 20D to the respective coverage areas 10(1)-10(N) of the remote antenna units 14(1)-14(N). Each remote antenna unit 14(1)-14(N) may include an RF transmitter/receiver (not shown) and a respective antenna 24(1)-24(N) operably connected to the RF transmitter/receiver to wirelessly distribute the communications services to client devices 26 within their respective coverage areas 10(1)-10(N).
With continuing reference to FIG. 1, the remote antenna units 14(1)-14(N) in the DAS 12 are also configured to receive uplink communications signals 20U in multiple frequency bands from the client devices 26 in their respective coverage areas 10(1)-10(N). The uplink communications signals 20U received in multiple frequency bands can be routed to different uplink path circuits (not shown) in the remote antenna units 14(1)-14(N) related to their frequency band. At the related uplink path circuits in the remote antenna units 14(1)-14(N), the uplink communications signals 20U can be filtered, amplified, and combined together into the combined uplink communications signals 20U to be distributed to the central unit 16. The central unit 16 can separate out the received combined uplink communications signals 20U into their respective bands to distribute to the base station 18.
Interference of downlink communications signals 20D and/or uplink communications signals 20U may occur in the DAS 12 due to non-linear signal processing components provided therein. For example, in the broadband DAS 12 in FIG. 1, signals in a frequency band of a given downlink communications signal 20D received and processed by a non-linear signal processing component in the central unit 16 may be duplicated as harmonics in other frequency bands falling within frequency bands of other received downlink communications signals 20D. For example, an 1800 MHz harmonic may be generated from a 900 MHz downlink communications signal 20D. Thus, when the downlink communications signals 20D in their respective frequency bands are combined in the central unit 16 to be distributed to the remote antenna units 14(1)-14(N), any harmonics generated from downlink communications signals 20D may interfere with other downlink communications signals 20D when combined. Similarly, when received uplink communications signals 20U are combined in a remote antenna unit 14(1)-14(N) to be distributed to the central unit 16, any harmonics generated from received uplink communications signals 20U may interfere with other uplink communications signals 20U when combined. Limiting input power to signal processing components is one method of limiting or avoiding harmonics caused by non-linearity. However, limiting input power can limit dynamic range of the DAS 12 in an undesired manner.
No admission is made that any reference cited herein constitutes prior art. Applicant expressly reserves the right to challenge the accuracy and pertinency of any cited documents.